<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>
    <div class="box1"></div>
</body>

</html>
<style>
    .box1 {
        width: 100px;
        height: 100px;
        background: #000;
    }
</style>